Furnace damper



y 5.1934. H. M. CUNNINGHAM 1,953,347

FURNACE DAMPER Filed July 31, 1931 I! TTO NEYS.

Patented May 1 5, 1 934 UNITED STATES PATENT OFFICE v 3 Claims.

This invention relates to furnace dampers and especially to check dampers for use in furnace installations of the type which are normally interrnittently operated.

In such installations, for example, a domestic heater of the oil burning type, it is desirable that the check damper be closed just after ignition of the fire or flame in order to increase the draft at this time and thus quickly heat up the chimney and lines or passes of the boiler or heater. Shortly after the fire has started, for example, two or three minutes, it is desirable that the check damper should again be opened so that the fire may burn most efficiently and without undue consumption of fuel or overheating of the flue.

Before proceeding with a description of the present invention, it should be noted that in addition to the desirable conditions referred to above, the check damper should remain open while the fire is not burning, that is, during such times as the thermostatic control which is normally provided is effective completely to turn off the fire or at least materially to decrease its intensity.

The present invention has in view the provision of a damper structure which is automatically actuated to provide the desirable combustion conditions outlined above.

The general invention, as well as objects and advantages in addition to those noted above, will be more apparent from a consideration of the following description making reference to the accompanying drawing in which- Figure 1 is a fragmentary side elevational view of a portion of a furnace or combustion chamber offtake or flue having the damper arrangement of the present invention applied thereto;

Figure 2 is a fragmentary detail view of a portion of the damper of Figure 1, the damper proper being here illustrated in closed position; and

Figure 3 is a view similar to Figure 2 but illustrating the damper proper in open position.

Referring, first, to Figure 1 in which the reference numeral 4 designates a portion of the furnace or combustion chamber olftake, it will be seen that a circular opening in the flue is provided with a cylindrical inlet casing 5 in which the check damper 6 is disposed.

The damper 6 is pivoted within the casing 5 as at 7-7, these pivots being arranged at different sides although not diametrically opposite to each other. That is, the damper is arranged for pivotal movement about an axis which divides the total area of the damper into unequal portions, in this instance the portion above the pivot line 7-7 being smaller than the portion therebelow.

For purposes of control of damper movements or position, I preferably employ a thermostatical- 1y operated latch or lock device which may be mounted either within or outside of the flue 4 or the casing 5, it being necessary only that the heat responsive element of the device be subject to changes in temperature of the gases in the flue. In the present instance, this device has been mounted inside the casing 5 so that it is subject to temperature changes within the fiue, at least in part by virtue of conduction through the metallic walls of the fiue 4 and casing 5.

This device includes a thermostatic bi-metal part 8 which is arranged for cooperation with a The part 8 is further constructed and arranged so that upon increase in temperature its inner end 10 moves downwardly to engage the latch member 9, the latter preferably being made of suitable spring metal so that after being forced downwardly (see Fig. 3) it will always return to the position indicated in Figure 2 upon decrease of the temperature of the thermostatic part 8.

As will be apparent from inspection and comparison of Figures 2 and 3, when the lock or latch 9 is depressed the damper 6 is free to open by swinging of the lower edge thereof inwardly. It will also be seen that in its upper position, the latch 9 is disposed to prevent opening of the damper.

A stop 11 may also be employed in order to prevent swinging of the upper side of the damper p0v inwardly as such action would interfere with proper operation of the arrangement for reasons which will be more apparent herebelow.

To consider the operation of the arrangement, consider first that the fire in the combustion chamber is burning at a normal rate. Under these circumstances the damper 6 will occupy the position shown in full lines in Figure 3 and, in addition, the parts 8 and 9 of the thermostatic control may occupy either the position illustrated in Figure 3 or the position of Figure 2, according to the temperature of the flue, flue gases and airdraft. At this time the damper is maintained in an open or a partially opened position by virtue of the draft action which has a greater effect 5 upon the lower and larger surface of the damper than upon the upper surface thereof.

When the flame or fire is extinguished, the drop in temperature in the fiue maintains the parts 8 and 9 in the positions indicated in Figure 2 or moves these parts to this position. It should be noted, however, that the action of the draft is still of sufficient force or effect to maintain the damper in an open position, and attention is further called to the fact that it is highly desirable that the damper remain open during the idle periods since this materially reduces the flow or passage of cold air through the passes or flues of the furnace. The passage of such cold air through the furnace itself, of course, is highly undesirable in view of the decided chilling which would result.

When the flame of the burner is again started or ignited, a condition somewhat resembling a small explosion is brought about within the passes of the furnace and also in the offtake. This explosion or rapid expansion of gases within the flue is of suflicient force to slam the damper :to closed position. The thermostatic parts 8 and 9, of course, at this time are disposed as illustrated in Figure 2, but since they are both of resilient character, the movement of the damper to closed position is not prevented. After this initial pressure increase in the flue, and the resultingclosing movement of the damper, the thermostatic part 8 is heated, usually within about two or three minutes, toa temperature such that the catch or look is again released, whereupon the damper, under the influence of the draft, opens as illustrated in Figure 3.

Thus, in accordance with the present invention, during the critical ignition or starting period, es-

.pecially of a domestic oil burning installation, the

ideal warming up conditions are provided, and at the same time the desirable conditions for normal operation,-as well as idle periods, are provided for. The foregoing steps, it is observed, are all brought about automatically so that the efficiency, particularly of domestic oil burning installations, is materially enhanced.

While I have described the structure and operation of the present invention in connection with an application thereof to a check damper in a furnace offtake, it should be understood that at leasta number of features of the invention may be applied with equal advantage to other damper arrangements. For example, the arrangement may be modified for application to a draft damper, i. e., one normally disposed in the air intake to the combustion chamber.

What I claim is 1. In combination with a flue having an opening therein, a damper movably mounted in said opening and a thermostatic device subject to the temperature of the gases in the flue for controlling damper movement, the damper being arranged for movement to closed position under the influence of rapid expansion of gases in the flue, and the thermostatic device including latch means arranged to maintain the damper in closed position below a predetermined flue temperature.

2. A check damper mechanism for a flue of an intermittently operating furnace, said mechanism including a damper member mounted for movement to open position under the influence of check air-draft and for movement to closed position, against said air-draft, under the influence of expansion of flue gases incident to initial operation or starting of the furnace, and a thermostatic control device. for the damper subject to the temperatureof the fluetgases, said device including latch means for retaining the damper in closed position when the flue is below a predetermined temperature and said device, including said latch means, further being arranged to permit movement of the'damper from open toclosedposition regardlessof the temperature in the flue.

3. In combination with a flue having an openpositioned to maintain the damper in closed position, and a thermostat responsive to temperature changes of the flue, said thermostat being operatively associated with said latch and so constructedand arranged asto release the latch upon increase in flue temperature above a predetermined point.

HAL M. CUNNINGHAM. 

